A. Field of the Invention
The present invention relates generally to the optical communications field, and, more particularly to a faceplate electrostatic discharge attenuating waveguide.
B. Description of the Related Art
Circuit board space (real estate) is at a premium in the optical communications field for a variety of reasons. First, many carriers or other consumers of optical communications equipment have a very limited floor space in which to place new equipment. For example, some carriers may only have a single open bay (or shelf) in which to place new equipment. If the communications equipment can be more densely packed, then a greater amount of equipment may be placed within the available space.
Another reason for the premium on circuit board real estate is the ever increasing number of channels that equipment vendors are attempting to squeeze into the available space. For example, DWDM (dense wave division multiplexing) equipment vendors relentlessly attempt to increase the number of channels that the equipment can handle. Since each channel typically requires a separate circuit board, the number of circuit boards and associated space requirements also increases with increasing channel counts.
In the optical communications field various connections must be made between the equipment and fiber. Conventional connectors are used to make these connections between the fiber and a module. It has been a common practice of many vendors to situate these connections behind an outer faceplate of the module in order to protect the module components from ESD (electrostatic discharge). The strength and frequency of the ESD passing through the openings in the faceplate is a function of three variables: the size of the opening, depth of the opening, and the strength of the source ESD generator. Indeed, there are a variety of industry standards that specify ESD tolerances. To meet these standards, a simple solution is to place the module components far behind the outer faceplate. As is also known in the art, the outer faceplate is part of a Faraday cage or conductive case shield that protects the components within from ESD.
FIGS. 1A and 1B show a conventional faceplate 10 and circuit board 30 arrangement. As shown, faceplate 10 has a front portion 12 integrally connected to a pair of side portions 14, 18. A plurality of openings 16 are provided in front portion 12, each opening 16 being sized to permit a bulkhead adapter 34 to be provided therein. Front portion 12 also includes a pair of retractable fasteners 20 for connecting faceplate 10 to a shelf (not shown) that houses faceplate 10 and circuit board 30. Side portion 14 has eight slots 22 (four pairs of two slots 22) provided therethrough for mounting spring fingers (not shown) thereon. The spring fingers provide grounding contact with adjacent modules, and along with faceplate 10 and the shelf, create a Faraday cage that protects the components within from ESD.
Side portion 14 further has a plurality of holes 24 for connecting faceplate 10 to a cover plate 28, via conventional fastening means, such as screws. Faceplate 10, circuit board 30, and cover plate 28 make up a module that may be slid into and out of an optical communications equipment shelf. The grounding contact between the spring fingers of adjacent modules, as well as the shelf, creates the Faraday cage that protects the components of circuit board 30 housed within the optical communications equipment shelf.
As best seen in FIG. 1B, circuit board 30 includes a plurality of transceivers 32 that mount onto circuit board 30. A transceiver is a combination transmitter/receiver in a single package. The term is used in reference to transmitter/receiver devices in cable or optical fiber systems. Each transceiver 32 includes a plurality of male or female connectors provided therein that align with a corresponding opening 16 provided in front portion 12 of faceplate 14 and receive corresponding male or female connectors and fibers. A bulkhead adapter 34, which is typically a female/female connector, is provided within each opening 16 of faceplate 10. A pair of fibers 36 with male connectors 38 connect to the female connectors provided in the portion of each bulkhead adapter 34 located outside of faceplate 10 (facing away from circuit board 30). Another pair of fibers 36′ with male connectors 38′ connect to female connectors provided in the portion of each bulkhead adapter 34 located inside of faceplate (facing towards circuit board 30). The opposite ends of fibers 36′ have male connectors 38′ that connect to female connectors provided within a corresponding transceiver 32. Transceivers 32 are provided in an interior portion of circuit board 30, away from the edges 30′ of circuit board 30. This way transceivers 32 lie within the zone of protection provided by the Faraday cage, described above, protecting transceivers 32 from ESD. The Faraday cage effectively attenuates almost all of the ESD emanating through openings 16 of faceplate 10 a distance of approximately 2¼ inches away from faceplate 10. Thus, the preferred spacing of transceivers 32 from the edges 30′ of circuit board 30 is 2¼ inches.
Although situating transceivers 32 far behind faceplate 10 typically solves the ESD problem, the practice creates another, separate problem. Namely, the space in front of transceivers 32 wastes valuable circuit board real estate. As mentioned above, this real estate is quite valuable particularly as circuit density and channel counts increase.